The present invention relates generally to information recording and/or reproducing systems; more particularly it relates to improved methods and means for positioning a transducer relative to a moving medium. The following U.S. Patents are of interest with respect to transducer positioning (servo) systems; U.S. Pat. No. 4,032,984 to Kaser; et al.; U.S. Pat. No. 4,027,338 to Kril; and the references referred to in these patents.
The present invention will be understood as commonly useful with magnetic disk recording and reproducing systems wherein one or more read/write heads are employed as transducers. Such systems are typically employed to provide auxiliary data storage in an automatic data processing system -- with the data being recorded on in a plurality of concentric circumferential tracks about the disk. The data in any particular track is read by positioning the associated read/write head radially of the disk so as to register with this track. Preferably the track number is verified before a transducing operation begins.
Preferably, such a head is, here, to be understood as positioned in two-steps; first, by invoking a "coarse" positioning sequence (also referred to as "track seeking") to move the head to a radial position within close proximity of the target track; then, invoking a "fine" positioning sequence to bring the head into precise registry with the target track and maintain this alignment (also referred to as "track following") while transducing along that track.
Workers in the art are familiar with various methods for such coarse and fine positioning -- such as the methods described in the above referenced patents. For instance, workers have used specially selected servo encoding patterns recorded along servo-sector portions of each track to indicate such coarse and fine positioning signals. Each such servo sector may contain a servo code including: a common reference transition, followed by "track-follow" servo data (e.g., for providing fine positioning with respect to two adjacent tracks); this followed by "track-seek" servo data to control coarse positioning of the transducer head.
The present invention involves improvements in such servo methods and means; improvements particularly apt for an "embedded" servo format (e.g., see cited patent to Kril) -- as opposed to a "dedicated" (sector or track) format. Workers will appreciate that an "embedded" format presents difficult problems as track density and/or bit density are increased. This invention addresses those problems.
More particularly, the instant features will be seen as apt for implementing certain servo data format. In this format, the fine servo data which comprises a "reference transition" followed by another opposite polarity transition at either a first or second position of each track depending on whether the track is odd or even -- thus recording an odd or even indicium at respective different relative located positions on adjacent tracks. And, in such a format, the coarse servo data comprises a track-group identification code in a series of successive data cells, each cell containing a single magnetic transition representating either a binary "0" or "1" depending on whether the transition occurs in the first or second half of the cell. Preferably, this coarse pattern employs a specially chosen sequence, such as a Gray code sequence, permitting only one change in the (magnetic transition) code between adjacent tracks. Also, such a code is preferably laid-down and manipulated, so that a "between track" condition is readily detectable, and results in detected pulses being obtained in both the first and second portions of the "changed cell".
Workers will understand that preferred embodiments of this invention will provide a high performance, high capacity, low cost (per megabyte unit) system; one able, for instance, to multiply the data capacity of a conventional disk storage system. Workers will also appreciate that these advantages are achieved using relatively conventional, readily available subsystems. For instance, disk systems improved by the taught features will be seen to provide a very high level of real bit density (for a "several hundred megabyte" capacity, the order of several megabytes, or more, per square inch) -- preferably in a configuration of relatively compact overall size and of very reasonable cost (e.g., one to two dozen cubic feet and costing just a few dollars per megabyte), along with very reasonable access-to-data times (e.g., the order of about three dozen ms.).